Modified homo- and copolymers of formaldehyde or trioxane and process for their manufacture



United States Patent rm. Cl. cos 37/02 U.S. Cl. 260-67 2 Claims ABSTRACTOF THE DISCLOSURE Manufacture of shaped articles of polyoxymethylenesand copolymers of formaldehyde and trioxane with cyclic ethers with theaddition of imidazole derivatives whereby the size of; the spherolitesin the polymers is reduced and their number per unit volume isincreased.

The present invention relates to modified homoand copolymers offormaldehyde or trioxane and to a process for their manufacture.

It is known that homoand copolymers of formaldehyde or trioxane have avery pronounced tendency towards crystallization. Even in the case of aslight undercooling of the melt a rapid growth of spherolites isobserved which are generally larger than the wave length of light and,therefore, impart a considerable opacity to the material. Moreover, dueto the crystallization process numerous cracks and fissures develop inthe interior of the material and on the surface. Owing to these cracksand fissures both the smoothness of the surface and the mechanicalproperties of the products are considerably impaired. The aforesaidflaws become the more pronounced the larger the individual spherolitesare which depends, inter alia, on the processing conditions.

From the treatise by C. F. Hammer, T. A. Koch and I. F. Whitney, J.Appl. Polymer Sci. 1 (1959), 171, chapter 3, it follows that, whenmicroscopic examinations of melt preparations of polymers .offormaldehyde which have been placed between glass as well as metalplates are carried out, there is no indication of artificial nucleation.

Now we have found that shaped articles of homoand copolymers offormaldehyde or trioxane with reduced spherolite size can be obtained inan advantageous manner by adding to the homoand copolymers prior to themolding process compounds of the formula in which X represents the groupC=O, NH or CONH, Ar represents benzene, naphthalene or diphenyl, and inwhich the total heterocyclic grouping may occur once or twice in themolecule, in an amount within the range of from 10" to 2X l0 percent byweight, preferably in an amount within the range of from to 10 percentby weight. Examples of preferred compounds are2,3-dihydroxy-quinoxaline, 2,6-dihydroxy-m-benzobisimidazole and2,2-dihydroxy-6,6-bis-benzimidazole.

By the addition of these compounds, which do not melt at the processingtemperatures of the polymer and which are only partially soluble in theliquid polymer, the structure of the polymer is essentially modified andthe number of spherolites per unit volume increased by one to threepowers of ten. It is remarkable that most of the additives that havebeen described as nucleating agents for polypropylene, for example, areentirely ineffective in the case of the homopolymers or copolymers offormaldehyde or trioxane.

By homopolymers of formaldehyde and trioxane there are to be understoodpolyoxymethylenes whose molecular weight is at least 10,000 and whose OHterminal groups are stabilized against thermal degradation byetherification or esterification. (Etherification of polyoxymethyleneswith alcohols in the presence of sulfuric acid: US. Patent 2,512,950;etherification of the terminal OH groups of polyoxymethylene withaliphatic acetals in acid solution: Belgian Patent 570,884;esterification of the OH terminal groups of polyoxymethylene with aceticanhydride: British patent specification 770,717.)

By copolymers of formaldehyde or trioxane there are to be understoodcopolymers of to 99.9 percent by weight of formaldehyde and 0.1 to 20%by weight of cyclic ethers, preferably of 80 to 99.9 percent by weightof trioxane and 0.1 to 20 percent by weight of cyclic ethers.

By cyclic ethers there are to be understood especially compounds of theformula in which R R R and R each represent hydrogen, an alkyl radicalor a halogen-substituted alkyl radical, and in which R represents amethyleneor an oxymethylene radical, an alkylor ahalogen-alkyl-substituted methylene radical, or an alkylor ahalogen-alkyl-substituted oxymethylene radical and n represents 0, l, 2or 3, or in which R represents (OCH CH --OCH n represents the integer 1and m represents 1, 2 or 3. The said alkyl radicals contain 1 to 5carbon atoms and can be substituted by 0 to 3 halogen atoms, preferablychlorine atoms.

As cyclic ethers there are preferably used ethylene oxide, glycol formaland diglycol formal. Propylene oxide, epichlorhydrin and4-chloro-methyl-dioxolane may also be used with advantage. Finally thereare also suitable cyclic or linear formals of long-chained a,w-dl0lS,for example butanediol formal or hexanediol formal.

The process according to the present invention is advantageously carriedout in such a manner that the substances indicated are distributed inthe pulverized polymer by means of a rapid mixer and shaped articles aresubsequently molded in the hot in the usual manner.

The advance in the art achieved by the method described above consistsin that the surface of the shaped article made from the polymers orcopolymers modified accord ing to the process of the present inventionis substantially improved. Furthermore, the number and the size of thecracks and fissures developing on the surface and also in the interiorare reduced considerably, whereby the mechanical strength and stiffnessare distinctly improved. It is due to these improvements that thehomopolymers or copolymers of formaldehyde or trioxane that have beenmodified according to the process of the present invention exhibitdistinct advantages in many industrially important fields of applicationas compared with the products used hitherto.

The following examples serve to illustrate the invention, but they arenot intended to limit it thereto.

Examples 1 to 8 (Examples 1 to 5 are comparison examples) 10 grams of apulverized copolymer of trioxane and 2% by weight ethylene oxide (a =1.2dl/g., measured in butyrolactone at C.), respectively, were mixedintimately with the substances indicated in Table 1 on a rapid analyticmill (Messrs. Janke and Kunkel). Of the mixture thus obtained,approximately 0.1 mm. thick films were pressed on a heatable moldingpress at 190 C. between hard chrome brass plates, which films wereallowed to cool at 100 C. for a period of 10 minutes. Moreover, severalmilligrams of the powder mixtures prepared as described above weremelted at approximately 220 C. between two cover glasses to yield a thinfilm which was allowed to cool at 100 C. for a period of 10 minutes. Asubstance was designated as nucleating agent if it produced spheroliteswhich were smaller in size as compared with the untreated sample.

4 Example 10 TABLE 1 Concentration Substance added (percent, Efli- Ex.Structural formula by weight) cieney 1 p'Tertiary-butyl benzoic acid2X10- oH3-o-coo11 I CH 2 Na-benzoate 2X10- 3 Terephthalic acid 2X10-rrooo-Qcoon 4 3-metl1yl-acridone 2X10- O H M I 5 Acridine 2X10 62,3-dihydroxy-quiuoxaline 2X10- N=C--OH N=GOH 72,fi-dihydroxy-m-benzobis-imidazole 2X10- K HO-C C-OH l l H H 82,2'-dil1ydroxy-G,6-bis-benzimidazole 2X10- Example 9 10 grams of apulverized homopolymer of formaldehyde with acetate terminal groups weremixed on a rapid analytic mill with 1 10- percent by weight of thesubstances enumeratcd in the Examples 1 to 8. Microscopic examinationsof films confirmed the order of efiiciency indicated in the last columnof Table 1.

Example 11 TABLE 2 Percent by weight of additive X10- Percent against100% of black glass standard. 79 85 Example 12 Due to the modifiedspherolite structure the mechanical properties of the polymer wereinfluenced. The properties of a copolymer of trioxane and 2% by weightof ethylene oxide with the addition of 2 1() percent by weight of thesubstance enumerated under (6) in Table 1 measured in comparison withthe untreated product are summarized hereunder. Stiffness and strengthof the treated product were distinctly higher than those of thecomparison product.

TABLE 3 Percent by weight of additive 2X1-2 Flexural stress (kp./cm.1,085 1,140 Stiffness in'torsion 120 (kp./cm. 1, 900 1,900 Tensilestrength (kp./cm.) 660 690 Ultimate tensile strength (kp./cm. .1 670 7301 Test specimen taken from injection-molded sheets.

2 Test specimen taken from pressed sheets.

We claim:

1. In a process for the manufacture of shaped articles of homopolymersof formaldehyde or trioxane or copolymers of formaldehyde or trioxanewith an oxygen containing cyclic ether of a ring size of from 3 to 14members, the improvement of which comprises adding to the polymer priorto molding to 2X1O percent by weight of a compound of the formulawherein Ar represents benzene, naphthalene or diphenyl, and in which thetotal heterocyclic grouping may occur once or twice in the molecule.

2. A thermoplastic molding composition consisting es sentially ofhomopolymers of formaldehyde or trioxane or copolymers of formaldehydeor trioxane with a cyclic ether of the formula in which R R R and R eachrepresent hydrogen, an alkyl radical or a halogen-substituted alkylradical from 1 to 5 carbon atoms, and in which R represents amethyleneor an oxymethylene radical, an alkylor ahalogenalkyl-substituted methylene radical, or an 'alkylor ahalogenalkyl-substituted oxymethylene radical and n represents 0, l, 2or 3, or in which R represents (OCH CH OCH n represents the integer 1and m represents 1, 2 or 3, and incorporated therein from 10- to 2 1O-percent by weight of a compound of the formula wherein Ar representsbenzene, naphthalene or diphenyl, and in which the total heterocyclicgrouping may occur once or twice in the molecule.

References Cited FOREIGN PATENTS 633,389 10/1963 Belgium.

WILLIAM H. SHORT, Primary Examiner.

L. M. PHYNES, Assistant Examiner.

US. Cl. X.R. 26045.8, 67.5

